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Black deposits on arb branches #927766

Asked April 07, 2026, 6:12 PM EDT

Hello, 3-4 year established south west facing arborvitae "emerald green" irrigation in area. While flushing out dead interior debris, I noticed near bottom, black on lower branches. Any idea?

Oakland County Michigan

Expert Response

It could be that irrigation is hitting it at that spot, or dogs are urinating on it. It could even be from salts, fertilizer or ice melt landing there.  I don't believe it insect or disease related, it will flush out new growth and this localized damage will disappear, as long as it's not periodic dog/irrigation related, in which case you would need to take corrective action. In the meantime, it can be pruned out to allow for new growth to refill in those areas.

Best of luck. 

Thank you for your question!  Replied April 08, 2026, 9:02 PM EDT

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